3nd Biennial Contemporary Clinical Neurophysiological Symposium October 12, 2013 Fundamentals of NCS and NMJ Testing Peter D. Donofrio, M.D. Professor of Neurology Vanderbilt University Medical Center
Disclosure Potential Conflict of Interest I have no financial relationships to disclose that are relative to the contents of this presentation.
Fiber type Pathology Temporal course Adapted from fig 1-2, Preston and Shapiro Goals of EDX Testing Localization Severity Muscle NMJ Nerve Anterior Horn
What are the indications for electrodiagnostic consultation/testing? Suspected neuromuscular disease Anterior Horn Cell Disorders Nerve root pathology Peripheral nerve/plexus pathology Neuromuscular junction pathology Muscle pathology
Value of NCSs/EMG When neuromuscular disease is present, electrodiagnostic testing can: Clarify the type of pathology (i.e. AHC, root, neuropathy, NMJ, or myopathy) Determine severity & extent of pathology Confirm site of pathology Estimate chronicity of pathology
Disorders Diagnosed/Evaluated by NCSs/EMG Generalized Neuropathies Axonal (Many etiologies) Demyelinating Acquired» Acute: GBS» Chronic: CIDP Hereditary Mixed Diabetic sensorimotor neuropathy Uremic neuropathy
Polyneuropathies Continued Polyneuropathies associated with many medical conditions Multiple investigations often needed NCSs/EMGs: best initial test to clarify underlying pathophysiology (i.e., axonal vs demyelination) Results may help focus rest of work-up
Disorders Diagnosed/Evaluated by NCSs/EMG Focal Neuropathies Carpal Tunnel Syndrome (median neuropathy at the wrist) Ulnar Neuropathy Peroneal Nerve Palsy Others: brachial plexus lesions, tarsal tunnel syndrome, etc.
Disorders Diagnosed/Evaluated by NCSs/EMG Radiculopathy Cervical Lumbar Motor Neuron Disease Amyotrophic lateral sclerosis (ALS) Spinal muscular atrophy (SMA)
Disorders Diagnosed/Evaluated by NCSs/EMG Muscle Disease Inflammatory Polymyositis, Dermatomyositis Metabolic Hereditary or Congenital
Disorders Diagnosed/Evaluated by NCSs/EMG Neuromuscular Junction Disease Myasthenia Gravis Lambert Eaton Myasthenic Syndrome Botulism Medications
Nerve Conduction Studies (NCSs) Technical Information Peripheral nerves are stimulated with an controlled electrical stimulus Responses recorded Compound motor action potential (CMAP) Sensory nerve action potential (SNAP) F wave H- reflex
Nerve Conduction Studies Motor Latency Measure of conduction time from nerve segment through neuromuscular junction to muscle fibers Sensory Latency Measure of conduction time of action potential across a nerve segment Conduction Velocity Measure of the velocity of the fastest conducting axons Motor Amplitude Measure of the number of activated axons and muscle fibers Sensory Amplitude Measure of the number of activated axons
Nerve Conduction: Late Responses F Wave Latency Retrograde rebound motor impulse Travels full length of motor axon and back Information about proximal segments Limited sensitivity/specificity H Reflex Afferent Path: Sensory axons (group Ia fibers) Efferent Path: Motor Axons (alpha motor neurons) Follows muscle stretch reflex arc Side to side latency most valuable
Normal Median Motor Study DL CV Amp (msec) (m/s) (mv) Wrist-APB 3.2 15.0 Elbow-Wrist 55 14.8
Types of nerve conduction Sensory: typically antidromic Typical nerves examined: Sural, ulnar, median, occasionally superficial radial, superficial peroneal studies
Sensory NCS Parameters Onset and peak latencies Conduction velocity determined by velocity of a few fast fibers Amplitude determined by the number of large sensory fibers activated
Normal Median Sensory Study 1 msec/div Latency CV Amp (msec) (m/s) (uv) Wrist-D2 2.2 58 44.1
F Waves Useful to assess proximal nerve conduction Helpful in the evaluation of: Radiculopathy Guillian-Barre Syndrome Peripheral neuropathy Other demyelinating neuropathies
F Waves: Normal Median
H Reflexes Useful to assess proximal nerve conduction Helpful in the evaluation of: Polyneuropathy S1 radiculopathy Upper Motor Neuron lesions
F-waves and H-reflex Useful for identifying proximal segmental demyelination Can only be done when motor amplitude is > 1 mv Height-dependent
Neuromuscular Junction Testing Repetitive Nerve Stimulation Stimulate nerve with train of supramaximal stimuli before and after exercise Record from muscle Attention to technical factors important More sensitive recording from proximal muscles
Repetitive Nerve Stimulation: Normal 3Hz stimulation
Myasthenia Gravis Repetitive Nerve Stimulation
Repetitive Nerve Stimulation Myasthenia Gravis
Single Fiber EMG Model of Potential Pairs
Limitations of NCSs/EMG Generally not helpful in the evaluation/diagnosis of: Pain from joint disease Fibromyalgia or myofascial pain syndromes Central nervous system disorders Disorders that do not arise from the neuromuscular system
What to Expect From an EMG Report The reason for the referral is addressed A clinically and physiologically relevant interpretation/diagnosis An outline of the localization, severity, and acuity of the process Notation of other diagnoses that are detected/excluded Explanation of any technical problems
What to Expect From an EMG Report Data obtained during the study: (NCS) Amplitude Distal latency Distance Conduction velocity Normal (Reference) data Side-to-side comparison (when appropriate) Limb temperature during the study
What to Expect From an EMG Report Data obtained during the study: (EMG) Presence & type of abnormal spontaneous activity Motor unit recruitment Motor unit morphology
EMG Pearls Electrodiagnostic studies are a supplement to, and not a replacement, for the history and physical examination Electrodiagnostic results are often timedependent Electrodiagnostic studies are not standardized investigations and may be modified by the practitioner to answer the diagnostic question
Pitfalls of nerve conduction studies Temperature effect and cold limb Sloppy measurement of distances Anatomic abnormalities of patient Technical factors: edema, large limbs, long limbs Too few nerve conduction studies, lack of comparisons Too many nerve conduction studies: Interpretation of non-existing abnormality